Electronic fluid pipeline leak detector and method

ABSTRACT

Disclosed is an instrument wherein the pressure or flow of a fluid in a pipeline is monitored with a voltage proportional thereto being electronically differentiated to determine whether any rate of change of pressure exists, which is often indicative of a leak in the pipeline. If a rate of pressure change of a predetermined extent exists for a predetermined period of time and if a total pressure change exceeds a predetermined value, an output signal can close a valve in the pipeline or can sound an alarm. In addition, in situations where a liquid is involved, a surge develops upon a line break, that is, a large rate of instantaneous pressure drop, and such surge can also be detected and appropriate remedial measures taken. The instrument is also capable of shutting down the pipeline in instances of inordinately low or high pressure conditions.

BACKGROUND OF THE INVENTION

This invention relates to a method and apparatus for detecting leaks influid pressurized vessels, the most typical being a pipeline. Moreparticularly, this invention relates to an electronic instrument andmethod of operation thereof, which can detect the rate of change ofpressure or flow and total pressure or flow change caused by a break orleak in a pipeline carrying a liquid or gas, and take remedial measurestherefor.

Fluids such as natural gas, oil or the like, are often transported overlong distances by pipeline. It is often important to quickly detectleaks or breaks in the pipeline, not only for a conservation of thefluid, but also in the case of flammable, toxic or like fluids, forsafety purposes. A break or leak is most often characterized by apressure drop over a period of time with some pressure drops being rapidand others being quite slow. The prior art is characterized by a numberof devices which attempt to detect the leak by monitoring this pressurechange. For example, U.S. Pat. Nos. 2,836,192 and 2,915,042 are typicalmechanical/pneumatic devices designed for that purpose. These types ofdevices are usually only workable with gas lines as opposed to liquidlines and can have certain drawbacks even when operating on gas lines.For example, these devices often fail to detect small rates of pressurechange, which, if existing over a long period of time, must be detected.Then too, these devices are susceptible to failure due to the pluggingof orifices, condensation in the rate tanks which changes the volumethereof, and corrosion of the various parts, the latter occurring whenthe pipeline is carrying a caustic or sour gas.

Some electronic devices have been developed in an attempt to avoid theaforementioned problems. These devices can satisfactorily detect changesin pressure over a period of time and if a greater pressure rate ofchange is detected than a preselected amount, remedial measures can betaken. However, if a change in pressure greater than the preselectedamount occurs, followed by a period of relative pressure stability,followed again by a change in pressure greater than the preselectedamount, etc., the total pressure drop would be indicative of a problemin the pipeline but would go undetected by this device. Similarly,fluctuations in line pressure, not resulting in an appreciable pressurechange could falsely activate these prior art devices.

Other systems for detecting leaks or breaks in pipelines have beendirected to detecting variations in the intensity of the sound of theflowing gas. These devices have met with little success in thatbackground noises are indistinquishable thus often causing false alerts.In addition, like the other prior art discussed above, these systems arenot applicable to liquids where a surge or large instantaneous rate ofpressure drop exists upon a break.

Additionally, none of the prior art of which I am aware provides theadditional feature of a means to shut down the system under inordinatelylow or high pressure situations whether or not a break is indicated.

SUMMARY OF THE INVENTION

It is thus an object of the present invention to provide a methodperformed by an electronic device which detects breaks or leaks inpressurized vessels such as a fluid pipeline.

It is another object of the present invention to provide a method anddevice, as above, which detects both the rate of pressure drop and thetotal pressure drop in the pipeline.

It is a further object of the present invention to provide a device, asabove, which is not susceptible to the problems encountered bymechanical pneumatic systems used for similar purposes.

It is still another object of the present invention to provide a methodand device, as above, which can be used for pipelines carrying a gas ora liquid.

It is an additional object of the present invention to provide a methodand device, as above, which can detect the instantaneous surge ofpressure change caused by a break or leak in a fluid carrying pipeline.

It is yet another object of the present invention to provide a methodand device, as above, which can monitor the flow of the fluid in thepipeline to determine the presence of a break or leak therein.

It is yet a further object of the present invention to provide a methodand device, as above, with the capability of detecting high or lowpressure pipeline conditions whether or not a break in the pipelineexists.

These and other objects of the present invention, which will becomeapparent from the following description, are accomplished byimprovements hereinafter described and claimed.

In general, in a method and apparatus for detecting irregularities in afluid pipeline, a characteristic, such as pressure or flow, of the fluidis monitored with an output signal proportional thereto differentiatedto produce a signal proportional to the rate of change of thecharacteristic. This signal is compared with a preselected maximumtolerable rate of change and when that maximum is exceeded, a signal issent to a timing device. If the signal is of a duration longer than apredetermined time, a signal is transmitted to a logic circuitpreferably in the form of a gate. In the meantime, the signalproportional to the rate of change is integrated to determine the totalchange of the characteristic. This total change is compared with apreselected maximum tolerable total change and when that maximum isexceeded, a signal is sent to the gate. Thus, if both conditions aremet, that is, a rate of change and total change both in excess of thepreselected tolerable maximums, remedial measures, such as closing avalve or sounding an alarm, can be taken.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a device according to the present inventionfor use with fluid pipelines.

FIG. 2 is a block diagram depicting an adaptation of the deviceaccording to the present invention specifically usable for liquidpipelines and in addition showing various adjuncts to the presentinvention whether used for a liquid or gas pipeline.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A fluid carrying pipeline 10 is shown in block form in FIG. 1 to carrygases or liquids usually at high pressures quite often over a longdistance. A "pipeline" is shown and referred to herein as the fluidcarrying vessel, it being understood that the subject invention couldhave utility with any pressurized vessel such as a fluid storage vessel.The pressure within pipeline 10 is desirably held at a substantiallyconstant pressure although often small pressure changes will occurwithout an attendant problem. However, if pipeline 10 should break ordevelop a leak, the pressure therein will change and corrective stepsshould be taken. A conventional transducer 11 in the preferred formmonitors pipeline fluid pressure, and "pressure" will be the fluidcharacteristic generally referred to throughout this description.However, it should be understood that other fluid characteristics, suchas flow, could be monitored without departing from the spirit of thisinvention.

The output of transducer 11, at point A, is thus a voltage signalproportional to fluid pressure. A conventional differentiator circuit 12receives the output of transducer 11 and differentiates the same so thatthe output, at point B, is a voltage signal which is proportional to therate of change of pressure with respect to time (^(d) p/dt). If thepipeline fluid pressure is constant, this signal will, of course, bezero. However, once a pressure change exists, a B signal of somemagnitude will correspondingly be created.

The output of differentiator 12 is received by a comparator 13 whichcompares the B signal proportional to pressure rate of change with apreselected signal proportional to a pressure rate of change set intocomparator 13. This preselected signal could be set at a maximumtolerable rate of change value, that is, a value which if exceeded wouldin and of itself be indicative of a potential pipeline problem. Theprior art would have used such a setting. However, because of otherfeatures of this invention, to be hereinafter described, this settingcan be set to detect small pressure fluctuations, on the order of about1/2 psi per minute without giving false alarms. When the B signalexceeds the preselected value, a timer 14, which can be a monostablemultivibrator, is activated by signal C out of comparator 13. Timer 14can have a variable time period or time delay set therein. That is,timer 14 can be set so that it will not "time out" for whatever perioddesired, typically ranging from thirty seconds to 180 seconds. Thus, ifafter that time period the C signal from comparator 13 is still beingreceived, an output signal D is exhibited by timer 14. if, however,during the time delay period, the rate of pressure change has droppedbelow the preselected level such that the C signal no longer exists, noD signal will be transmitted by timer 14. Rather, timer 14 will merelybe automatically reset to await another C signal.

The B signal out of differentiator 12 is also fed to a conventionalintegrator 15 which, as is well known in the art, electronically takesthe integral of its input signal. Thus, the output of integrator 15, E,is a voltage proportional to the total change in pressure sensed bytransducer 11. This E signal is fed to a comparator 16 which comparesthe E. voltage with a preselected signal proportional to a totalpressure difference set into comparator 16. This preselected signal isset at a maximum tolerable total pressure difference value, that is, avalue which if exceeded indicates a potential pipeline problem. Thisvalue should be high enough so that small pressure differentials notassociated with a break or leakage will be ignored. In pipelines runningat about 700 psi, a total pressure change of from 5 to 30 psi is atypical setting dependent on the sensitivity desired. When the E signalexceeds that preselected value, comparator 16 puts out a signal Findicative of such.

The D signal out of timer 14 and the F signal out of comparator 16 arefed to a logic circuit 17 which could be an OR gate but which most oftenwill be an AND gate. As such, logic circuit 17 will only exhibit anoutput signal G when it receives both a D and an F signal. In effectthis means that a G signal will exist only when there has been a totalpressure change in excess of the preselected value set into comparator16 and a rate of pressure change in excess of the preselected value setinto comparator 13 for a predetermined period of time as dictated by thetime delay set into timer 14. In the circuit of FIG. 1, when suchconditions are satisfied, the G signal actuates remedial measuresthrough actuator 18 which can be, for example, a solenoid valve whichwould operate to close the pipeline until the problem could be found orcan be an audio or visual alarm which would alert the operator to theproblem.

In an example of the operation of the circuit of FIG. 1, it will beassumed that the pipeline is operating at 700 psi, that the preselectedpressure rate of change set into comparator 13 is 1/2 psi per minute,that the time delay set into timer 14 is 30 seconds, and that themaximum tolerable total pressure drop set into comparator 16 is 5 psi.If now a break in the pipeline occurs, transducer 11 senses the changein pressure and differentiator 12 determines the rate of change ofpressure. For this example assume that the rate of change, that is, theB signal, is 2 psi per minute. Comparator 13 would immediately sensethat the rate of change was greater than its 1/2 psi per minute and theC signal would start timer 14. After 30 seconds, if the 2 psi per minutepressure drop continued to exist, the D signal would appear to the logicAND gate 17. In the meantime integrator 15 would be calculating thetotal pressure drop E but after 30 seconds that total pressure drop willonly be 1 psi and thus comparator 16 will not exhibit an F signal andlogic circuit 17 will not exhibit the actuating G signal. In thismanner, if the pressure drop had been due to something other than a linebreak, for example, a compressor in the line might have been shut downcausing a small pressure drop of short duration, corrective measureswould not be taken. But after 21/2 minutes of a 2 psi per minute drop,comparator 16 would sense that the five psi setting has been exceededand exhibit the F signal which coupled with the already existing Dsignal would take corrective measures. In this manner only drops inpressure above a predetermined amount and above a predetermined ratewill be recognized but line fluctuations which could be minor will beignored.

In FIG. 2, circuitry is displayed which could be operated in and ofitself or which ideally could be an adjunct to the circuit of FIG. 1.For clarity, a number of FIG. 1 circuit elements are repeated in FIG. 2,it being understood that some of the identical elements of FIG. 1 couldbe employed or additional separate elements could be utilized. When apipeline, designated by the numeral 10' in FIG. 2, is carrying a liquid,a special phenomenon exists upon the occurrence of a break or leak. Apressure surge is created in the fluid, this surge being characterizedby an essentially instantaneous pressure drop, that is, an extremelyhigh rate of pressure drop but only a small overall pressure drop. Sucha drop may go undetected by the circuit of FIG. 1 in that whilecomparator 13 would sense the drop, the total drop would not be largeenough to exceed the setting of and thereby activate comparator 16.

To detect such a surge, transducer 11', like transducer 11, monitors thepressure in the line having an output A' proportional thereto. Adifferentiator circuit 12' receives the A' signal and differentiates thesame so that its output, B', is a signal which is proportional to therate of change of pressure with respect to time (^(d) p/dt). Acomparator 13' receives the B' signal and like comparator 13 comparesthis signal with a preselected maximum tolerable rate of change. Becausecomparator 13' should be set to detect the surge phenomenon, the settingthereof can usually be in the neighborhood of 100 to 300 psi per second.When such is exceeded by a surge, a signal H could immediately initiateremedial measures through actuator 18' or as shown in FIG. 2, could besent to a logic circuit 19. Logic circuit 19, in the form of aconventional OR gate, would be employed if the surge circuit justdescribed were used in conjunction with the FIG. 1 circuit or othercircuits yet to be described. Thus, as shown in FIG. 2, if the circuitof FIG. 1 were to be used with the surge circuit, the G signal from FIG.1 could be sent to the logic OR gate 19 before going to the actuator. Inthis instance then, either a surge signal H or the signal G wouldinitiate the remedial measures.

It should be evident that by employing the OR logic 19, othercharacteristics of the pipeline can be used to control actuator 18'. Forexample, the A or A' signal indicative of pressure can be fed to a highpressure comparator 20. This comparator also receives a predeterminedset signal corresponding to a maximum tolerable pipeline pressure. Ifthe A signal would exceed that maximum, as I signal indicative of suchwould be sent from comparator 20 to logic circuit 19 and the system shutdown by actuator 18 or 18' so that the cause of the high pressure couldbe determined and corrected.

Similarly, a low pressure comparator 21 can receive the A or A' signaland compare it with a predetermined set signal corresponding to amaximum tolerable low pressure in the pipeline. If the A signal would gobelow that predetermined signal, a J signal indicative of intolerablelow pressure in the pipeline would be sent from comparator 21 to logiccircuit 19 and the system shut down by actuator 18 or 18' so that thecause of the low pressure could be determined and corrected.

Thus, four individual circuits, the circuit of FIG. 1, the surgecircuit, the high pressure cutoff circuit and the low pressure cutoffcircuit, can selectively initiate the corrective measures throughactuator 18. It should be evident that this can be done through the ORgate logic 19 or could be done by four individual module-like circuitseach having their own actuator. In addition, if desired, the logic 19could be in the form of an AND gate such that the actuator 18 would notinitiate corrective measures until any number or all of the circuitsindicated the existence of a problem.

It should thus be evident that the device disclosed and method ofoperation thereof enables one to monitor pipeline characteristics andtake remedial measures when a predetermined intolerable situation existsthus substantially improving the pipeline control art.

We claim:
 1. A system for detecting irregularities in a fluid carryingpipeline or the like comprising; transducer means monitoring acharacteristic of the fluid in the pipeline and providing an outputsignal proportional thereto; differentiator means receiving the outputsignal of said transducer means and providing an output signalproportional to the rate of change of said characteristic with respectto time; first comparator means receiving the output signal of saiddifferentiator means, comparing that output signal with a preselectedrate of change of said characteristic with respect to time and providingan output signal when the output signal of said differentiator meansexceeds said preselected rate of change; timing means receiving theoutput signal of said first comparator and providing an output signalafter a predetermined time delay; integrator means receiving the outputsignal of said differentiator means and providing an output signalproportional to the total change of said characteristic; secondcomparator means receiving the output of said interator means, comparingthat output signal with a preselected total change of saidcharacteristic and providing an output signal when the output of saidintegrator means exceeds said preselected total change; said outputsignal of said timing means and said output signal of said secondcomparator being indicative of an irregularity in the fluid pipeline ofsufficient size to warrant correction.
 2. A system according to claim 1wherein said characteristic of the fluid is pressure.
 3. A systemaccording to claim 1 wherein said characteristic of the fluid is flow.4. A system according to claim 1 wherein said timing means is amultivibrator and the output signal thereof is only provided if saidmultivibrator is still receiving the output signal of said firstcomparator after the predetermined time delay.
 5. A system according toclaim 1 further comprising logic means receiving said output signal ofsaid timing means and said output signal of said second comparator andproviding an output signal indicative of the irregularity in the fluidpipeline.
 6. A system according to claim 5 wherein said logic means isan AND gate which provides an output signal only if receiving a signalfrom both said timing means and said second comparator.
 7. A systemaccording to claim 5 further comprising actuator means receiving theoutput signal of said logic means.
 8. A system according to claim 7wherein said actuator means is a solenoid valve operable to close thepipeline.
 9. A system according to claim 1 wherein said characteristicof the fluid is pressure and the preselected rate of change isapproximately 1/2 psi per minute, the preselected total change isapproximately in the range of 5 to 30 psi, and the time delay isapproximately in the range of thirty to 180 seconds.
 10. A method fordetecting irregularities in a fluid carrying pipeline or the likecomprising the steps of monitoring a characteristic of the fluid in thepipeline, from the monitored characteristic determining a rate of changeof said characteristic with respect to time, comparing said rate ofchange with a predetermined rate of change, timing the period that therate of change exceeds the predetermined rate of change for apredetermined time period, from the monitored characteristic determiningthe total change of the characteristic, comparing said total change ofsaid characteristic with a predetermined total change, and takingcorrective measures in said pipeline when the rate of change exceeds thepredetermined rate of change for the predetermined time period and thetotal change of said characteristic exceeds the predetermined totalchange.